<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
  function f(n) {
      if (n==1||n==2){
          return 1;
      }
     return f(n-1)+f(n-2);

    }
   alert(f(10));
</script>
</body>
</html>